Some people prepare for Shark Week by shopping for JAWS t-shirts, shark tooth earrings, and even shark fin cupcake toppers for their viewing parties, but swimmer Michael Phelps has other plans. Phelps retired from competitive swimming after the 2016 Olympic Games in Rio de Janeiro, but this summer he’ll be challenging a bigger game. On July 23, he’ll be racing head-to-head against a great white shark.

But even history’s greatest swimmer needs some help racing one of the ocean’s fastest predators. So, Phelps will be strapping on an appendage that will bring his body one step closer to resembling a fish.

“I was able to have a fin — a monofin,” he said in an interview with Time on Tuesday. “That helped me make the race a little bit closer.”

After all, the most decorated Olympic medalist of all time is still only human. Compared to the shark, Phelps’s world records are a joke. Even at his fastest, Phelps can only swim at a rate of 5 1/2 miles per hour. A great white shark can go six to seven miles per hour during a leisurely swim and can top out at 25 to 35 miles an hour when it hunts.

Michael Phelps Monofin race  pool
Michael Phelps will be wearing a monofin during his race against a great white shark.

Strapping on a monofin will even the playing field, to some extent. These ridged fins are made of lightweight plastic, or even carbon fiber, and strap on in a matter of seconds, effectively giving the wearer a mermaid tail. Like the caudal fins of fish and dolphins, the monofin works by displacing the water surrounding it in a more efficient way than bare human feet would when they paddle. Pushing water back with the fin propels the wearer forward.

Phelps will be using the Lunocet, a brand of monofin invented in 2002 by fin designer Ted Ciamillo. The Lunocet, Ciamillo tells Inverse in an e-mail, “accurately replicates the swimming morphology and even the jointed mechanism of the peduncle that dolphins employ to attain such efficient speed.”

In other words, Phelps’s fin will work in the same way as a dolphin’s tail: by creating a proper angle of attack with a lifting foil and by regulating vortices through a trailing edge flexibility gradient. The key to the Lunocet, explained West Chester University of Pennsylvania marine biologist Frank Fish, Ph.D., who collected the data that Ciamillo later used in his design, is that it acts like an underwater wing to create a “lift force” — the force perpendicular to the direction that the fluid is flowing (in this case, upward). That force is converted to thrust, pushing the moving object forward.

monofin lift force
The monofin generates a "lift" force in the water, propelling the wearer forward.

As Scientific American noted in 2009, early tests with the Lunocet on regular swimmers showed that they could reach speeds of up to eight miles per hour.

But even with the monofin, Phelps has a lot of work ahead of him. Sharks are much more efficient swimmers compared to other fish, producing twice as many jets of water when they move their fins side to side, as Harvard researchers showed in a 2011 study in Proceedings of the Royal Society B. In this study, biomechanist Brooke Flammang, Ph.D., studied the water displacement patterns of small sharks by placing them in tanks where water flowed constantly, so they could swim in place. When she added small reflective particles to help visualize the water movement, she and her team noticed that the sharks produced two rings of twirling water as their tails moved from one side to the other. Most fish, she noted, only produce one. Sharks, she concluded, are more efficient swimmers because this extra thrust of water — produced when sharks stiffen their tails midswing — gives them a boost.

While we won’t know how much faster Phelps will swim with the monofin until Shark Week, we’re pretty sure that, even if it doubles his already-incredible speed, he’s going to get owned. Still, it’ll be a treat just to see the world’s greatest swimmer channel his inner merman.

Photos via Discovery Channel, Wikipedia, Flickr / marcopako , Flickr / jayhem